IL92951A - Fire extinguishing method and apparatus - Google Patents

Description

FIRE EXTINGUISHING METHOD AND APPARATUS FIELD OF THE INVENTION This invention relates to fire control systems.

BACKGROUND OF THE INVENTION Fire control systems having a plurality of different types of detector connected to a logic system which is responsive to the detector outputs for operating suppression means are well known. Typically, each detector is adapted to detect a different property characterising a fire such as, for example, smoke, heat, U.V. and I.R. radiation and so on. Since any one of these properties by itself is not necessarily indicative of the presence of a fire, the logic system determines the presence of a fire based on several detector signals exceeding predetermined thresholds.

Prior art fire control systems employ one of a number of suppression agents determined, usually, by the fire source and the type of equipment which is being protected. Thus, for example, whilst water is very commonly employed on account of its availability, it is not suitable for extinguishing organic liquid fires such as, for example, petroleum for which organic chloro-fluoro hydrocairbons are typically used.

There exist several drawbacks with such suppression agents. Thus, for example, even when water is suitable as an extinguishing agent, it often causes irreparable damage to the protected equipment, whilst organic extinguishing agents are expensive and need to be stored in pressurised vessels, and may cause hazards to personnel and damage the ozone layer in the atmosphere.

It is known that flames themselves can be influenced by an external field applied across the flame. It has been shown that the influence of an electric field on a flame is due to the concentration of positive and negative ions and electrons in the flame which is particularly high in the flame formation zone. However, the principles of field interaction with flames have not been completely clarified.

It is clear that the substitution of conventional suppressants in a fire control system by an electric, magnetic or electromagnetic field adapted to extinguish the fire, would offer many advantages over conventional fire control systems employing conventional suppressants.

SUMMARY OF THE INVENTION It is an object of the invention to provide a fire control system wherein an electric field is employed for extinguishing a fire.

According to the invention, there is provided a fire control system, comprising: at least one first detection means for detecting a respective property characterising a fire and providing a corresponding first signal in response thereto, logic means coupled to the or each first detecting means and responsive to the or each first signal for generating a second signal indicative of a fire, and electromagnetic suppression means coupled to the logic means and responsive to the second signal for applying an electromagnetic field across a base of the fire of a magnitude and polarity to extinguish the fire.

The electromagnetic suppression means comprises a source of high voltage connected between a positive electrode disposed at the base of the fire and a negative electrode displaced from the positive electrode such that the resulting electric field intersects the fire near the base. Preferably, the negative electrode is in such a form that the applied electrical field encircles the fire and is directed normal to the contour of the fire.

All fires require a source of fuel which, upon igniting, can create flames which disperse from the source whilst being sustained thereby. The term "base" of the fire relates to the flame formation zone corresponding to the area wherein the fire is ignited. It has been found that the fire is most susceptible to the influence of an applied electric field across its base.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of non-limiting example only with regard to a fire control system employing electromagnetic suppression means, and with reference to the accompanying drawings, in which: Fig. 1 is a block diagram showing a system according to the invention; Fig. 2 is a block diagram showing a detail of a detector unit for use in the system shown in Fig. 1; Fig. 3 is a flow diagram of a logic circuit for use in the system shown in Fig. 1; Fig. 4 is a pictorial representation showing schematically a system according to the invention for controlling fires in distribution pipes; Fig. 5 is a pictorial representation .showing schematically a system according to the invention for controlling fires in storage vessels; Fig. 6 is a pictorial representation showing a system according to the invention for controlling fires resulting from spillages of flammable materials; and Fig. 7 is a pictorial representation of the system shown in Fig. 6 when used on an enlarged scale.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring to Fig. 1, there is shown a block diagram of a fire control system according to the invention. A detector unit 10 is provided containing at least one detector for detecting a respective property characterising a fire and providing a corresponding first signal in response thereto. The detector unit 10 is coupled to a logic circuit 11 which is responsive to each of the first signals produced by the detector unit 10 and which is adapted to generate a second signal indicative of a fire.

Coupled to an output of the logic circuit 11 are high voltage (H.V. ) suppression means 12 energised by a high voltage (H.V. ) power supply 13 so as to apply a high voltage across respective negative and positive electrodes (not shown) in the high voltage suppression means 12. The resulting high voltage establishes an electric field in a location wherein a fire has been detected.

Referring to Fig. 2, the detector unit 10 is shown to comprise a plurality of detectors, including a U.V. sensor 15 for detecting ultraviolet radiation, an I.R. sensor 16 for detecting infra-red radiation, a heat sensor 17 and a particle sensor 18 for detecting particles such as soot. The I.R. sensor 16 includes two ranges of sensor responsive to far infra-red and near infra-red, respectively.

An output of the detector unit 10 is coupled to a microprocessor 25 corresponding to the logic circuit 11 shown in Fig. 1. Thus, the microprocessor 25 is responsive to each of the first signals generated by the sensors 15, 16, 17 and 18 for generating a second signal indicative of a fire in the event that the respective first signals are of a magnitude commensurate with the outbreak of fire. By including a plurality of sensors and ensuring that the microprocessor 25 is responsive to each of the sensors, the incidence of false alarms is significantly reduced.

Fig. 3 shows a flow diagram relating to operation of the logic circuit 11 shown in Fig. 1. The H.V. power supply 13 is constituted by an electrical pulse generator having three modes of operation: (1) OFF, (2) STANDBY and (3) ENABLED. The H.V. power supply 13 is responsive to the first signals generated by the detector unit 10 for going into STANDBY mode. In the event that the logic circuit 11 generates a second signal corresponding to outbreak of a fire, the H.V. power supply 13 is ENABLED and generates a high voltage.

The logic circuit 11 is also adapted to determine the location of a fire by analysing which detectors in a given volume generate first signals of sufficient magnitude commensurate with the outbreak of fire. Thus, whe large spaces are to be protected, a plurality of detector units are installed, each monitoring a relatively small volume of the total space. The logic circuit 11 is then adapted to generate respective second signals only in respect of those detector units whose first signals are of sufficient magnitude. Thus, in the event that the logic circuit 11 determines the presence of a fire in one or more specific location, an enabling signal is sent to the H.V. suppression means 12 which is coupled to an electrode module 30 such that the H.V. power supply 13 is connected across only those electrodes corresponding to the location or locations wherein the fire has been detected.

During the process of extinguishing the fire, the detector unit 10 and associated logic circuit 11 continue, respectively, to monitor the fire's progress and to analyse the effectiveness of the H.V. suppression means 12. In this manner, by means of suitable feedback means, the voltage generated by the H.V. power supply 13 and connected across the electrode module 30 may be increased until the fire is extinguished. Likewise, in the event that a fire spreads from one location to another, further electrode modules may be energised corresponding to the new location of the fire. When the fire is completely extinguished, a STOP signal is -sent to the H.V. suppression means 12 and the H.V. power supply 13, thus switching off the H.V. power supply 13.

Fig. 4 shows pictorially a specific implementation of a fire control system according to the invention for use in a distribution pipe 36 carrying a .flammable liquid therein. There is shown a plurality of control units 35a, 35b and 35c adapted to be coupled at each end to corresponding sections 37a, 37b, 37c and 37d of the pipe 36. The control unit 35a comprises a tubular section of substantially the same diameter as the pipe 36 and adapted to be screw fitted thereto. Around an outer wall of the control unit 35a there is disposed a plurality of first detectors 38a which are coupled to a central logic and power supply (not shown). Similarly, second detectors 39a are disposed around an inner wall of the control unit 35a and are likewise connected to the central logic and power supply.

Located within the control unit 35a is an annular electrode 40a whilst encircling the outer wall of adjacent sections of the pipe 36 are respective external electrodes 41a, 41b, 41c, 41d in the form of a circular wire mesh, the internal and external electrodes being connected to respective supply rails in the central logic and power supply. The pipe 36 is formed of an electrically conductive material and constitutes a ground electrode 42 connected to the central logic and power supply.

The control unit 35a operates as follows. The first detectors 38a are adapted to produce respective third signals in respect of predetermined stimuli outside the pipe 36 whilst the second detectors 39a are responsive to corresponding stimuli within the pipe 36 for producing respective fourth signals. Each of the detectors is connected to the central logic and power supply which analyses the respective third and fourth signals produced by each of the detectors and determines (1) whether a fire has occurred and, if so, (2) its location. By location is meant either outside or inside the pipe 36 or both and, additionally, in which section or sections 27a to 37d of the pipe 36. In the event that a fire is detected by the first detectors 38a outside the pipe 36, the central logic and power supply applies a high voltage pulse between the wall of the pipe 36 constituting the ground electrode 42 and the respective wire mesh electrodes 41a or 41b on either side of the control unit 35a such that the high voltage negative supply rail of the central logic and power supply is connected to the wire mesh electrodes 41a, 41b.

In the event that a fire is detected by the second detectors 39a inside the pipe 36, the central logic and power supply applies a high voltage pulse between the wall of the pipe 36 and the respective internal electrode 40a such that the high voltage positive rail is connected to the internal annular electrode 40a.

In case where the pipe 36 is formed of an electrically insulating material, a separate ground electrode must be provided between the external mesh electrodes 41a to 41d and the internal annular electrode 40a.

The principles of such an embodiment are equally suitable for controlling fires caused in storage containers, such as drums and the like, containing flammable liquids. Fig. 5 shows a substantially cylindrical storage tank 45 having two sections 46a and 46b interconnected by a control unit 47 substantially identical to the control unit 35a, 35b and 35c describer above with reference to Fig. 4 of the drawings. Thus, the control unit 47 comprises a plurality of first detectors 48a, 48b, 48c, 48d and 48e disposed around an external periphery of the control unit 47 for detecting respective properties characterising a fire outside the storage tank 45 and a like plurality of second detectors (not shown) disposed around an internal periphery of the control unit 47 for detecting respective properties characterising a fire within the tank 45. The first detectors 48a to 48e produce respective third signals which are fed via a detector bus 50 to a central logic and power supply unit 51. Likewise, the second detectors produce corresponding fourth signals which are fed to the central logic and power supply 51 via the detector bus 50. The central logic and power supply 51 is adapted to analyse the incoming third and fourth signals in order to determine an outbreak of fire and, if appropriate, its location.

Depending upon the size of the storage tank 45, there may also be provided identical control units 52 and 53 displaced from the control unit 47 and having corresponding first and second detectors coupled to the central logic and power supply unit 51 by the detector bus 50.

The control unit 47 also includes an annular electrode 55 therein (constituting an internal electrode) connected via an internal electrode bus 57 to the central logic and power supply 51. In identical manner, the control units 52 and 53 include internal annular electrodes 59 and 60 which are connected through a wall of the storage tank 45 to the internal electrode bus 57.

Surrounding the whole of the storage tank 45 is a wire mesh 61 (constituting an external electrode) which is connected to the central logic and power supply 51 via a connection 62. The wall of the storage tank 45 is formed of an electrically conducting material which constitutes a ground terminal 64 which is also connected to the central logic and power supply 51.

In Fig. 5, the plurality of first and second detectors connected to the control units 52 and 53 are not shown, since they are identical in all respects to those shown in the first control unit 47. Likewise, the detectors as well as the internal electrodes are shown connected to the central logic and power supply 51 by respective buses although, in reality, separate connections are employed in order that the central logic and power supply unit 51 is able to analyse the incoming detector signals separately and apply a high voltage between the ground terminal 64 and a selected one or ones of the internal electrodes 55, 59 and 60 in the event that an internal fire is detected.

In the event that a fire is detected external to the storage container 45 by one or more of the plurality of external detectors, a high voltage is applied by the central logic and power supply 51 between the ground terminal 64 and the external wire mesh electrode 61 so as to apply an electric field between the wire mesh electrode 61 and the whole of the storage tank 45.

In both cases, the polarity of the applied voltage is such that the ensuing electric field completely encircles the base of the fire, the base itself effectively constituting the positive electrode.

Additionally, detectors may be provided on the external and internal surfaces of a lid (not shown) so that . a fire occurring anywhere within the drum is monitored. For large diameter storage vessels, the external wire mesh electrode may be provided in the form of a plurality of mutually electrically insulated mesh electrodes each of which is adapted to apply an electric field across a small area of the storage vessel. By segmenting the external electrode in this manner, an external fire may be extinguished without applying a high voltage electric field around a complete periphery of the storage container.

Fig. 6 shows a support platform 90 for supporting thereon fuel pipes, storage drums or other flammable equipment in order that a fire which occurs as a result of spillages of a flammable material may be extinguished using a fire control system according to the invention. The platform 90 comprises an electrode module 91 formed of metal and having therein a plurality of apertures 93a, 93b, 93c and 93d which define a like plurality of annular electrodes 95a, 95b, 95c and 95d. The upper section 91 is placed on an identically shaped lower section 98 formed of an electrically insulating material which is placed on a ground plate 100. Thus, in the event of a spillage, the flammable liquid flows into the apertures of the support platform 90 so as to be encircled by the annular electrodes in the electrode module 91.

A plurality of detectors (not shown) is connected to the support platform 90 for monitoring the outbreak of fire in one or more of the apertures 95a to 95d and being connected to suitable control logic for operating H.V. suppression means in the event of a fire being detected. The H.V. suppression means applies a high voltage pulse between the electrode module 91 connected to the negative supply rail and the ground plate 100 connected to the positive supply rail, thereby encircling the base of the fire with a high voltage electric field so as to extinguish the fire.

By supporting equipment in such a manner, a fire caused by a spillage is effectively sectlonallsed so that a large fire is reduced to a plurality of relatively small fires, each of which may be extinguished by the application of a high voltage pulse as described.

Fig. 7 shows a practical implementation of the embodiment described above with reference to Fig. 6 for protecting a large area of storage space. A plurality of support assemblies 101 is shown connected end to end so that good electrical contact is established between adjacent pairs of annular electrodes. Discrete areas of floor space are covered in this manner and between each discrete area of floor space the corresponding support assemblies are electrically insulated from each other by means of suitable insulation 102. The whole of the floor area is covered by a single ground plate 105 which, together with each of the annular electrodes corresponding to each discrete area of floor space, are connected to a central logic and power supply 107.

A plurality of detectors 108 are provided for monitoring each section of floor area so that in response to corresponding signals generated by the detectors 108, the central logic and power supply 107 is adapted to determine (1) the occurrence of a fire and (2) its location. A high voltage pulse is then applied between the positive ground plate 105 and the negative annular electrodes relating to the section or sections wherein a fire has been detected.

The invention thus permits a variety of different types of fire to be extinguished using H.V. suppression means and allows large fires to be divided into a plurality of relatively small fires which permit their extinction without subjecting the whole of a monitored space to an applied electric field.

It will be appreciated that whilst the invention has been described with particular reference to the application of a high voltage electric field in order to extinguish the fire, a similar result may be obtained by applying a magnetic or electromagnetic field or, indeed, a combination of electric, magnetic and electromagnetic fields.

It will also be understood that the invention can be employed together with conventional chemical extinguishing agents or with any other fire suppressant (e.g. inert gases). When employed in this manner, the intensity of a fire may be reduced by the electromagnetic suppression means, permitting the fire subsequently to be extinguished completely by the application of conventional chemical extinguishing agents. Such an arrangement permits a fire to be extinguished with a much lower volume of conventional chemical agents than is possible without the prior application of electromagnetic suppression means, thereby permitting the chemical extinguishing agent to be stored in relatively low volume vessels and reducing the resulting cost thereof.

Finally, it will be appreciated tht whilst the invention has been described with particular reference to a fully automatic fire control system, the use of electromagnetic suppression means is equally suitable for use with manual or semi-automatic systems. By "manual" is meant that the fire suppression means are adapted to be applied manually by an operator on his own initiative. By "semi-automatic" is meant that the logic means determines an outbreak of fire but merely provides an alarm of such outbreak without itself operating the electromagnetic suppression means. In this case also, the electromagnetic suppression means are operated manually.

Claims (6)

PA 92951/2 -13- CLAIMS :

1. A method of extinguishing a fire, characterized in: generating an intense electric field; and directing said electric field to the base of the fire until the fire is extinguished.

2. The method according to Claim 1 , wherein said electric field is generated by applying a high voltage between two electrodes separated by an air gap.

3. The method according to Claim 1 , wherein said electric field is directed to the base of the fire by initially locating the electric field at a location which would be in the vicinity of the base of a fire should a fire occur.

4. The method according to Claim 1 , wherein said electric field is directed to the base of the fire by mounting the electric field generator on a portable unit and manually directing the electric field to the base of the fire.

5. Apparatus for extinguishing a fire, characterized in that it includes: a generator for generating an intense electric field; and means for directing said electric field to the base of the fire until the fire is extinguished.

6. The apparatus according to Claim 5, wherein said generator includes two electrode structures spaced by an air gap, and means for applying a high voltage to said two electrode structures to produce an electrical discharge therebetween.